Integrated circuits have traditionally operated with a standard power supply of around 5 V. However, the growing need to reduce the size of integrated circuit-based electronic systems has led the designers of such circuits to reduce the standards for lithography and therefore for the power supply of transistors. Thus, transistors powered at 3 V or 1.8 V, for example, are used today.
However, it takes time to standardise supply voltages, and reducing the supply voltage is not given the same priority in all applications of the electronics industry. Therefore, currently, in an MOS integrated circuit, there are generally two voltages and two types of associated transistors. The inputs/outputs of these circuits are powered at a higher voltage than that powering their core. Thus, the input/output transistors are called “high-voltage transistors” and the core transistors are called “low-voltage transistors”. The low-voltage transistors are smaller and can therefore be more densely integrated.
Two categories of electronic circuits are currently differentiated:
in the first category, the circuit includes, for its inputs/outputs, transistors powered at 5 V (called 5-V transistors) and, for its core, transistors powered at 3 V (called 3-V transistors);
in the second category, the circuit includes, for its inputs/outputs, transistors powered at 3 V and, for its core, transistors powered at 1.8 V (called 1.8-V transistors).
The 3-V or 1.8-V transistors of these circuits cannot reliably support the voltage supply of 5 V. Indeed, a 3-V transistor can support a maximum voltage of 3.6 V applied between its various components: drain, source, gate and case. Similarly, a 1.8-V transistor can support a maximum voltage of 2 V applied between its various components.
The circuits of the second category are made according to a newer and more precise technology (with patterns of approximately 0.18 μm) and are therefore more efficient than the circuits of the first category.
As the power supply of all of the circuits (first and second categories) is generally 5 V, it is suitable to use voltage regulators (also called voltage regulator systems) providing other voltage supplies (3-V and 1.8 V).
Thus, for a circuit of the first category, a 5V-3V voltage regulator is used, made with 5-V transistors integrated into the circuit, and enabling a voltage of 3 V to be provided from the 5-V power supply. This regulator is easy to produce because a circuit of the first category includes 5-V transistors at the level of its inputs/outputs. Indeed, the same technology and the same process steps can be used to produce both the 5-V transistors of the regulator and those of the inputs/outputs.
However, for a circuit of the second category, it is necessary to have two voltage regulators: a first 3V-1.8V regulator that is easy to produce so that it is integrated into the circuit (due to the presence of the 3-V circuit at the level of the inputs/outputs of the circuit), and a second 5V-3V regulator. This second regulator is not as easy to produce as the 3V-1.8V regulator due to the absence of the 5-V transistor at the level of the inputs/outputs.
A first known solution for producing the second 5V-3V regulator in a circuit of the second category consists of integrating, at the level of the inputs/outputs of the circuit, 5-V transistors so as to produce an integrated regulator such as that used for the circuits of the first category. However, to provide both 5-V transistors (of the regulator) and 3-V transistors (of the remainder of the inputs/outputs) in the inputs/outputs of such a circuit, it is necessary to implement a mixed technology that is expensive and involves a large number of process steps (compared with a single technology).
A second known solution is to use a 5V-3V regulator outside the circuit and produced through 5-V transistors. However, this technique is also expensive and bulky because the regulator is not integrated into the circuit.